A wide variety of signal systems exist which signal the occurrences of various events. For example, signal systems exist which signal the occurrence of a vehicle moving to or from a particular location; a door, window, a latch or other selectively closable structure being opened or closed; a lock, a clasp (such as a seatbelt) or other selectively engageable structure being engaged or disengaged, etc.
Many of such signal systems have one or more limitation or constraint, e.g., they cannot efficiently convey information regarding a large number of structures, the structures cannot be freely moved long distances or relative to each other because the signal systems require electrical connections to power supplies, the signal systems a powered by batteries which require occasional replacement, etc.
For instance, various types of known devices are used for detecting the opening and/or closing of doors, including switch-type, optical-type and infrared type sensors. The use of these monitoring devices has several significant limitations-for example, false alarm rates (e.g., events triggered by exterior motion/vibration or movements caused by wind or thermal warming), as well as these devices being observable by third parties. Another significant limitation shared by these devices, and a downfall of many security and monitoring systems, is their requirement for a continuous power source, typically supplied by connecting to the structure's alternating current power supply or incorporating a battery power source, to transmit or relay information. This limitation restricts the choice and placement of sensors used in a security or monitoring system, as well as requiring routine maintenance, such as battery replacement, and long wiring runs.
It would be a benefit in a wide variety of situations to be able to provide a signal system which overcomes such limitations and constraints, e.g., to be able to mount a signal system on each of a plurality of storage containers (which are, for example, being carried on a ship), each signal system being free from wires connecting to a power source, and each signal system not relying for power on batteries, but being capable of generating a signal upon the occurrence of a specific event, e.g., the container on which the signal system is mounted being opened, or to be able to mount a signal system on each of a plurality of windows and/or doors, each signal system being free from wires connecting to a power source, and each signal system not relying for power on batteries, but being capable of generating a signal upon the occurrence of a specific event, e.g., the window or door on which the signal system is mounted being opened, or to be able to mount a signal system in a plurality of locations in a roadway, each signal system being free from wires connecting to a power source, and each signal system not relying for power on batteries, but being capable of generating a signal upon the occurrence of a specific event, e.g., a vehicle passing over any one of the locations in the roadway where a signal system is located. In addition, it would be a benefit to provide such a system which makes it possible for each signal to identify the particular signal system from which it was generated-for example, where a plurality of signal systems are mounted in respective storage containers, a signal generated by any of the signal systems is unique, such that the signal identifies which one of the storage containers has been opened.